The present invention relates to the field of parts made of 3D woven composite material. The present invention relates in particular to estimating the thickness to be given to such a part when designing the part.
Document FR 2 892 339 describes fabricating a composite turbine engine blade by using a 3D woven composite material. The main fabrication steps are as follows:                fabricating a mold having an inside surface that corresponds to the outside surface of the blade to be fabricated;        then inserting a 3D woven preform into the mold; and        finally injecting resin into the mold and then hardening the resin.        
During a prior step of computer-assisted design (CAD), the number of layers in the preform and the shapes of the layer exits in the preform that is to be inserted in the mold are determined, in particular as a function of the shape of the mold. Algorithms exist for performing such calculation. Those known algorithms use as input data a mean profile, also referred to as a skeleton profile, representing the shape of the part that is to be fabricated, in association with a thickness field representing the thickness of the part. On the basis of the shape of the mold, is it therefore necessary to determine the mean profile of the part and the corresponding thickness field.
For that purpose, in the context of fabricating a part made of 2D woven composite material, Document EP 2 327 538 proposes determining the thickness of the blade by projecting a point of its outside surface onto a plane parallel to the root of the blade, in a direction that is normal to the curve defined by the intersection between the above-mentioned plane and the mean profile of the blade.
Nevertheless, the behavior of a 3D woven composite material is different from that of plies of 2D woven material, and it has been observed that estimating thickness in that way is not appropriate and can lead to variations of fiber content, and thus to a part that is not very homogeneous.
Document FR 2 916 529 describes an optical method of measuring the outline of a part. That document does not relate in any way to designing a part made of 3D woven composite material. A passage of that document describes determining the outline of the part, but it makes no mention of a 3D woven preform nor does it make any mention of determining a number of layers or exit positions for such layers.